1. Field of the Invention
This invention relates to a car power source apparatus that powers the driving motor of an electric vehicle such as a hybrid car or electric car, and specifically relates to a car power source apparatus provided with a leakage current detection circuit to detect leakage current.
2. Description of the Related Art
In a car power source apparatus that powers an electric vehicle, it is necessary to produce a high voltage to increase output power. This is because output power is proportional to the product of the voltage and current, and because the higher the voltage, the more favorable the response when the motor is activated. For example, output voltage of a power source apparatus to drive a hybrid car or electric automobile is extremely high such as 200V or more. In a high voltage power source apparatus, there is a danger of electric shock for a hands-on mechanic during maintenance work. Therefore, from safety considerations, the power source apparatus is not electrically connected to the chassis. Consequently, to detect electric shock and disconnect the power source apparatus from other circuitry, the ability to detect leakage resistance is provided. Leakage resistance is resistance between the power source apparatus and the chassis. A car power source apparatus that detects leakage resistance is cited in Japanese Patent Laid-Open Publication No. 2006-25502.
FIG. 1 shows the detection circuit to detect leakage resistance of the power source apparatus cited in Japanese Patent Laid-Open Publication No. 2006-25502. The leakage detection circuits 80 shown in this figure have series circuits 91 of leakage detection resistors 92 and leakage detection switches 93 connected to battery 82 connection nodes 90. There are two sets of series circuits 91. The first series circuit 91A and the second series circuit 91B are connected to different connection nodes 90, 90. Further, the leakage detection circuits 80 are provided with voltage detection circuits 94 to detect the voltage developed across the leakage detection resistors 92. The leakage detection switches 93 of the first series circuit 91A and the second series circuit 91B are alternately switched on allowing the leakage detection circuits 80 to detect leakage resistance.